The Biting Habits of Leptoconops bequaerti. II. Effect of Meteorological Conditions on Biting Activity; 24 Hour and Seasonal Cycles

This paper investigates some of the factors which contribute to changes in the biting rate of Leptoconops bequaerti with time, i.e. inter-period variation. These include daily and seasonal cycles of activity and the influence of meteorological conditions on biting. Data for analysis were obtained from: (1) Two standardization experiments (i) in the morning-4 collectors x 8 periods of 15 min x 4 trials and (ii) at sunset-4 collectors x 4 periods x 5 trials. (2) Two 48-h sessions of continuous observation with one collector operating at a time. (3) Weekly early morning collections (from dawn +40 or +60 to +115 min) from 5 February 1960 to 10 February 1961. The main findings were: (a) L. bequaerti is diurnal, biting from dawn until sunset with maximum activity occurring between 08.00 and 09.00 hours. Another, but less intense, spell of biting takes place in the late afternoon (15.40-17.15 hours; sunset 17.55 hours). There is considerable day-to-day variation. (b) L. bequaerti is present throughout the whole year and in 1960-61 showed two periods of peak abundance in August and February with low numbers occurring in May-June and December. This seasonal cycle is probably related to rainfall. (c) The biting rate of L. bequaerti is affected less by meteorological conditions than that of any other ceratopogonid studied so far. It bites freely in the open at wind speeds of 10-12 miles/h but disappears when the wind reaches 15 miles/h. (d) Multiple regression analysis was used to investigate the quantitative relationship between biting rate and four meteorological variables (wind speed, temperature, illumination and saturation deficit) using data from (1) and (2) above. Wind speed was the most important factor but its inhibiting effect was masked by the positive stimuli provided by temperature and illumination. Saturation deficit had no effect on the biting rate. The calculated partial regression coefficients on log biting rate were: The regression accounts for 57.4% of the observable variation, when population changes are excluded, but, when this is impractical, only 15.9-30.3% of the variation can be attributed to meteorological factors. (e) The weekly biting rates of L. bequaerti were standardized with the partial regression coefficients to the following standards: This reduced variation among the weekly observations by 23.4% (between weeks 24.5%; within weeks 21.0%). (f) There was no correlation between biting rate and tidal range. (g) After standardization, the